Frogs living near farms can develop resistance to a commonly-used insecticide, scientists report in Evolutionary Applications.

When farmers spray insecticides on their fields, the chemicals don’t just kill bugs — they can harm other “non-target” animals too. Amphibians are particularly vulnerable because they’re also threatened by diseases, invasive species, and shrinking habitat. If amphibians could evolve to fight the toxic effects of pesticides, they’d have a better chance of survival.

The researchers collected wood frog eggs from nine populations and raised tadpoles in the lab. Then they tested the animals’ responses to chlorpyrifos, a common insectide, and Roundup, a herbicide. When exposed to chlorpyrifos, wood frogs that came from areas near farms had a higher survival rate, the team found.

Next, the researchers tested whether this resistance came at a cost. They placed the tadpoles in outdoor wading pools, some of which also contained a caged predator — a dragonfly — or extra tadpoles competing for food. Being chlorpyrifos-resistant didn’t appear to affect the tadpoles’ growth or their performance in the presence of predators or competitors. — Roberta Kwok | 3 May 2013